1. Field of the Invention
The present invention relates to a foam dispensing pump container for foaming a foamable liquid product such as shampoo, hand soap, cleaning solutions, hair-care product or shaving cream by depressing a nozzle member fixed to an upper end of a piston member of the container and pumping the foamable liquid with air into a mixing chamber, mixing the foamable liquid with the air in the mixing chamber, and homogenizing the foam through a porous member such as a net member and dispensing the homogenized foam from the nozzle member to the outside of the container.
2. Description of the related Art
The applicant has proposed several foam dispensing pump containers of the aformentioned type as disclosed in International patent application publication No. WO 92/08657 and Japanese patent application laid-open publication No. 293568/1992.
In these publications there is disclosed a foam dispensing pump container comprising: a double cylinder which is provided inside an opening portion of a container containing a liquid and which is constituted by an air cylinder and a liquid cylinder, both being arranged concentrically; a dip tube extending from a bottom portion of the liquid cylinder to a bottom portion of the container; a piston body constituted by air and liquid pistons, both pistons being arranged concentrically and integrally to move up and down in the air and liquid cylinders respectively; a hollow bent nozzle member provided at an upper end of the piston body and having nose portion, a stem and a foam passage; and air passage formed in an upper gap between the liquid piston and the air piston for allowing the foam path and an interior of the air cylinder to communicate with each other; a liquid passage formed in the liquid piston for allowing the foam passage and an interior of the liquid cylinder to communicate with each other; a second check valve disposed in an upper end of the liquid passage; a first check valve disposed at the lower end of the liquid cylinder; sheet-shaped porous members disposed in a mixing chamber communicating with the air passage and the liquid passage and in the foam passage downstream of the mixing chamber; an urging spring for urging the piston body upwardly to a top dead position with respect to the double cylinder; an air hole formed in the air cylinder to introduce an outer air outside the container into the container; and a lid member for fixing the double cylinder to the container and guiding insertion of the piston body therethrough, a suction hole provided in an upper wall portion of the air piston for introducing the outer air into an air chamber, defined by the air cylinder and the air piston, through an insertion gap between an outer circumferential surface of the air piston and an insertion hole of the lid member; a third check valve with a valve member provided in an upper wall portion of the air cylinder for opening and closing the suction hole.
The embodiment of the aforementioned foam dispensing container disclosed in the above publication bulletins uses a ball valve as the third check valve and its ball is so mounted, in the lower portion of the suction hole formed in the upper wall portion of the air piston, that it can move up and down by a predetermined amount between a valve seat on the lower surface of the circumferential edge portion of the suction hole and a projection for preventing the ball from coming off. As a result, unless the air chamber is pressurized, the ball stays seated on the projection by its own gravity, leaving the suction hole open for introducing the outer air into the air chamber, so that the outer air is promptly introduced without substantial resistance. When the interior of the air chamber is pressurized, on the other hand, the ball is urged upwardly to come into close contact with the valve seat and close the suction hole. As the air passage and the air chamber are always in communication with each other, the pressurized air in the air chamber is smoothly introduced into the mixing chamber through the air passage.
However, our subsequent investigations have revealed that the foam dispensing pump container thus constructed has the following disadvantages.
In case the nozzle member, or the pistons are depressed very slowly in foam dispensing operation, pressure in the air chamber may not rise high enough to urge the ball of the third check valve against its own gravity and force the ball to come into close contact with the valve seat. As a result, the air in the air chamber is released through the suction hole, so that no air can be fed to the mixing chamber by the time the nozzle member (or the piston member) bottoms out in its downward movement.
As the nozzle member (or the piston member) goes down, on the other hand, the foamable liquid in the liquid chamber, defined by the liquid cylinder and the liquid piston, is pumped into the mixing chamber through the liquid passage and, as no air is fed to the mixing chamber, the result is that no foam is dispensed from the nozzle member. Moreover, the portion of the foamable liquid fed to an interior of the mixing chamber but not dispensed from the nozzle member may flow down through the air passage and stay in the air chamber.
If these operations are repeated, the foamable liquid may be accumulated in the air chamber to such extend that air and the foamable liquid or just the foamable liquid is pumped from the air chamber when the nozzle member is depressed at an ordinarily desirable speed. As a result, the mixing chamber receives a mixture of air and the foamable liquid or just the foamable liquid from the air chamber, and undesired wet foam or unfoamed liquid is dispensed.
Normally, as the nozzle member (or the piston body) goes up after a dispensing action, the air chamber is subjected to a negative pressure so that air is sucked through the third check valve. However, if the third check valve picks up the foamable liquid accumulated in the air chamber, as described above, movement of the ball is disturbed due to the generally viscous nature of the foamable liquid, and functions of the third check valve may be lost, i.e., the ball may not be released from the valve seat completely so that air may not be sucked adequately. On such occasion, foam or foamable liquid in the mixing chamber may be drawn through the air passage and accumulated in the air chamber which is subjected to a negative pressure, as the mixing chamber communicates with the air chamber, resulting in undesirably thick foam containing a high ratio of liquid.